Peeling failure in beams strengthened by plate bonding. A design proposal

Existing experimental research has shown that the application of externally bonded laminates to strengthen reinforced concrete (RC) structures can lead to brittle failures involving debonding of the laminate before the design load is reached and a classical failure mode occurs. In an externally bonded RC beam, this peeling failure can initiate either near mid-span owing to the effects of flexural or shear cracks, or at the laminate end as a result of stress concentration at the laminate cut-off point. The design procedure to obtain the laminate area to strengthen a RC element should avoid these premature peeling failures. Therefore, there is a need to understand the mechanics of the laminate debonding process in order to prevent it. The evolution of the debonding process can be analysed by using non-linear fracture mechanics assuming a bilinear constitutive law for the interface. The crack propagation process is described through the evolution of different stages, in which the interfacial shear stresses can be obtained. As the transfer of stresses from laminate to concrete through the interface is a critical parameter in the correct performance of externally bonded structures, the transferred force should be limited to a maximum value in order to prevent peeling failure. A shear-bending interaction diagram based on this maximum transferred force associated with peeling failure is the main point of the design proposal presented in this paper.